It is known that so-called “shock control bumps” (SCB's) are useful to reduce the characteristic impedance of an aircraft wing. Shock control bumps are a relatively new class of flow control devices that offer a number of potential performance benefits for (transonic or supersonic) applications where shock waves are present. They have most commonly been considered as a means for improving the performance of transonic wings, through the manipulation of the air flow over the upper wing surface where near-normal shockwave exists, resulting in a reduced characteristic impedance of the aircraft wing and an improved buffeting behaviour.
As the name suggests, conventional SCB's consist of a physical bump placed on the aerodynamic surface where shockwave is known to occur. By far the most common application considered is the upper surface of a transonic wing. In this application SCBs can have a beneficial smearing effect on the structure of the near normal shockwave close to the wing surface. Specifically, SCB's split the shock into a number of weaker (oblique) shocks or compression waves that decelerate the flow more gradually (and hence more isentropically) than the single uncontrolled shockwave, thus incurring a reduced stagnation pressure loss and lower drag. A typical SCB consists of a ramp upstream of the nominal shock location, followed by a short crest region and then a tail. The ramp generates an oblique shock (or multiple oblique compression waves) and the main shockwave which deflects the incoming supersonic flow away from the surface. Around the crest region, the flow is decelerated to subsonic velocities by a near-normal shockwave, before the tail brings the post-shock flow back to the aircraft wing surface.